In Hernandez, et al. U.S. Pat. No. 5,269,759 an apparatus and method are disclosed for facilitating balloon catheter exchange in the vascular system of a patient. The balloon catheter is advanced along a guidewire through the artery of a patient. Then, if there is a need to remove the catheter without displacing the position of the guidewire, a first magnetic element (such as ferromagnetic material, permanent magnetic material, or any other material that is capable of attracting or being attracted by a magnet) on the guidewire is retained by a second magnetic element which is located proximate to the balloon catheter and not fixed thereto. Thus, the balloon catheter may be withdrawn, enclosing the end of the guidewire in its lumen, while the guidewire is retained by the magnetic force exerted between the first magnetic element carried on the guidewire and the second magnetic element, which is typically located outside of the balloon catheter.
Also, Scimed Life Systems, Inc. of Maple Grove, Minn. has offered to the market a device under the name "The Magnet" in which a series of magnets in a housing surround a special guidewire, which is also manufactured by the same company, to fix the position of the guidewire by magnetic force as a catheter is withdrawn.
However, there is a need to provide a magnetic retention member for guidewires which provides a stronger magnetic field, to reduce the risk that a catheter being advanced or withdrawn breaks the magnetic bond which retains the guidewire, causing it to advance or retract with the catheter.
Also, conventional guidewires require a proximally mounted magnetic unit, to be effectively retained by a magnetic retainer as their proximal ends are surrounded by a moving catheter.
By this invention, a magnetic exchange device is provided which may be attached to guidewires which are of conventional design, and which have no significant magnetic retention capability, since, typically, guidewires are made of a nonmagnetic stainless steel. Thus, by this invention, if it becomes necessary to remove a conventional catheter overlying a guidewire in a patient's arterial system without removal of the guidewire, this can be accomplished by this invention even with a conventional, nonmagnetic guidewire without the use of a very long and inconvenient guidewire extension such as the extension disclosed in Gambale et al. U.S. Pat. No. 4,917,103.